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IP Subnet Calculator - Calculate IP Subnets and CIDR Online

Last updated March 22, 2026

What is IP Subnetting?

IP subnetting is the practice of dividing a network into smaller sub-networks (subnets). This improves network performance, security, and management by organizing IP addresses into logical groups. Subnetting uses subnet masks to determine which portion of an IP address represents the network and which represents the host.

CIDR (Classless Inter-Domain Routing) notation provides a compact way to specify IP addresses and their routing prefix. For example, 192.168.1.0/24 means the first 24 bits are the network portion, leaving 8 bits for hosts (256 addresses, 254 usable).

Key Subnetting Concepts

Network Address: First IP in subnet, identifies the network
Broadcast Address: Last IP in subnet, sends to all hosts
Usable Hosts: IPs between network and broadcast addresses
Subnet Mask: Defines network and host portions
CIDR Notation: Compact format (e.g., /24 = 255.255.255.0)
Wildcard Mask: Inverse of subnet mask, used in ACLs

Example: 192.168.1.0/24

Network Address: 192.168.1.0
Broadcast Address: 192.168.1.255
Usable Range: 192.168.1.1 - 192.168.1.254
Total Hosts: 256 (254 usable)
Subnet Mask: 255.255.255.0

How to Use the IP Subnet Calculator

Step 1: Enter IP Address

Input any IP address within the subnet you want to calculate. The calculator works with any IP in the range, not just the network address. For example, 192.168.1.50 with /24 gives the same subnet as 192.168.1.0/24.

Step 2: Specify Subnet

Enter either CIDR notation (e.g., 24) or subnet mask (e.g., 255.255.255.0). The calculator accepts both formats and converts between them automatically.

Step 3: Review Results

The calculator displays network address, broadcast address, usable host range, total hosts, and other subnet details. Use this information for network planning, configuration, or troubleshooting.

Understanding the Output

Network address is used in routing tables. Broadcast address sends packets to all hosts. Usable hosts are IPs you can assign to devices. The first and last IPs (network and broadcast) cannot be assigned to hosts.

Common Use Cases

1. Network Planning

Calculate how many hosts a subnet can support before implementing a network. Determine if you need to split a network into smaller subnets or combine subnets for more hosts.

2. IP Address Assignment

Find the usable IP range for assigning addresses to devices. Ensure you don't accidentally use the network or broadcast address, which would cause connectivity issues.

3. Router Configuration

Configure router interfaces with correct network addresses and subnet masks. Verify that subnets don't overlap and routing is configured properly.

4. Firewall Rules

Create firewall rules using CIDR notation to allow or block entire subnets. Calculate wildcard masks for ACLs (Access Control Lists) on Cisco devices.

5. Cloud Infrastructure

Plan VPC (Virtual Private Cloud) subnets in AWS, Azure, or GCP. Calculate subnet sizes for different tiers (web, app, database) ensuring no IP conflicts.

Subnet Calculation Examples

Example 1: /24 Network (Class C)

IP: 192.168.1.0/24
Subnet Mask: 255.255.255.0
Network: 192.168.1.0
Broadcast: 192.168.1.255
Usable Range: 192.168.1.1 - 192.168.1.254
Total Hosts: 256 (254 usable)

Example 2: /16 Network (Class B)

IP: 172.16.0.0/16
Subnet Mask: 255.255.0.0
Network: 172.16.0.0
Broadcast: 172.16.255.255
Usable Range: 172.16.0.1 - 172.16.255.254
Total Hosts: 65,536 (65,534 usable)

Example 3: /28 Network (Small Subnet)

IP: 10.0.0.16/28
Subnet Mask: 255.255.255.240
Network: 10.0.0.16
Broadcast: 10.0.0.31
Usable Range: 10.0.0.17 - 10.0.0.30
Total Hosts: 16 (14 usable)

Example 4: /30 Network (Point-to-Point)

IP: 10.0.0.0/30
Subnet Mask: 255.255.255.252
Network: 10.0.0.0
Broadcast: 10.0.0.3
Usable Range: 10.0.0.1 - 10.0.0.2
Total Hosts: 4 (2 usable)
Use Case: Router-to-router links

Example 5: /8 Network (Class A)

IP: 10.0.0.0/8
Subnet Mask: 255.0.0.0
Network: 10.0.0.0
Broadcast: 10.255.255.255
Usable Range: 10.0.0.1 - 10.255.255.254
Total Hosts: 16,777,216 (16,777,214 usable)

Frequently Asked Questions

What is CIDR notation?

CIDR (Classless Inter-Domain Routing) notation is a compact way to specify IP addresses and routing prefixes. The number after the slash (/) indicates how many bits are used for the network portion. For example, /24 means 24 bits for network, 8 bits for hosts.

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